Method of forming a high K metallic dielectric layer

ABSTRACT

A process for forming a high dielectric constant, (High K), layer, for a metal-oxide-metal, capacitor structure, featuring localized oxidation of an underlying metal layer, performed at a temperature higher than the temperature experienced by surrounding structures, has been developed. A first iteration of this process features the use of a laser ablation procedure, performed to a local region of an underlying metal layer, in an oxidizing ambient. The laser ablation procedure creates the desired, high temperature, only at the laser spot, allowing a high K layer to be created at this temperature, while the surrounding structures on a semiconductor substrate, not directly exposed to the laser ablation procedure remain at lower temperatures. A second iteration features the exposure of specific regions of an underlying metal layer, to a UV, or to an I line exposure procedure, performed in an oxidizing ambient, with the regions of an underlying metal layer exposed to the UV or I line procedure, via clear regions in an overlying photolithographic plate. This procedure also results in the formation of a high K layer, on a top portion of the underlying metal layer.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] The present invention relates to methods used to fabricatemetal-insulator-metal capacitor structures for semiconductor integratedcircuits, and more specifically to a method used to form a highdielectric constant, (high k), metallic oxide layer, for use as adielectric layer for a capacitor structure.

[0003] (2) Description of Prior Art

[0004] Metal-Oxide-Metal, (MOM), capacitor structures are commonly usedin current analog/RF circuits. The use of an insulator layer, with ahigh dielectric constant, (high K), would be useful in terms ofproviding efficient charging for the analog devices. Therefore capacitordielectric layers, such as silicon nitride, with a dielectric constantof about 7, has been used in place of silicon oxide dielectric layers,featuring a dielectric constant of only about 3.9. For enhancedcapacitor performance, metal oxide layers, with dielectric constantseven larger than silicon nitride values, are now being considered foruse in MOM structures. However to form reliable, (in terms of breakdownstrength), metal oxide layers, such as tantalum pentoxide, (Ta₂O₅), oraluminum oxide, (Al₂O₃), temperatures greater than 400° C., are needed.These elevated temperatures however, can result in degradation toexisting interconnect structures, comprised of aluminum basedmetallurgies. The exposure of these aluminum based structures, totemperatures needed to form the metal oxide layer, can result inpre-melting, or reflowing of these structures.

[0005] This invention will describe processes used to form reliable,dense, metal oxide layers, for MOM structures, still however avoidingthe exposure of the surrounding interconnect structures, metalstructures other than MOM structures, to elevated temperatures. A firstiteration will describe local heating of an area of a metal layer, in anoxidizing environment, accomplished via local laser ablation. The laserablation process results in only surface heating of an underlying metallayer, allowing the desired region of metal to be oxidized, forming thedesired metal oxide layer at temperatures greater than temperaturesexperienced by surrounding metal structures. A second iteration willdescribe the localized formation of the metal oxide layer, in anoxidizing environment, using energy supplied by either UV or I lineexposures. Conventional photolithographic plates are used to allowspecific regions of an underlying metal layer to experience the UV or Iline exposure. Prior art. such as Kang in U.S. Pat. No. 5,834,357, aswell as Sun et al, in U.S. Pat. No. 5,930,584, describe processes usedto fabricate high K dielectric layers, however these prior arts do notfeature the unique processes used in this invention to achieve metaloxide layers, without exposure of surrounding metal structures to thehigh oxidation temperatures, used to form reliable, dense metal oxidelayers, on local regions of a metal layer.

SUMMARY OF THE INVENTION

[0006] It is an object of this invention to form a high K dielectriclayer, for a metal-oxide-metal, (MOM), capacitor structure, viaoxidation procedures, which allows the oxidizing region to experience ahigher temperature than the surrounding metal interconnect structures.

[0007] It is another object of this invention to form a high Kdielectric layer, via a laser ablation procedure, performed to localizedregions of an underlying metal layer, in an oxidizing ambient.

[0008] It is still another object of this invention to form a high Kdielectric layer via exposure of localized regions of an underlyingmetal layer, to UV or I line energies, in the presence of an oxidizingenvironment.

[0009] In accordance with the present invention a method of fabricatinga metal-oxide-metal, (MOM), capacitor structure, featuring a high Kdielectric layer, formed from localized heating of an underlying metallayer, is described. A first iteration of the invention initiates withthe deposition of an underlying metal layer, for subsequent use as thebottom electrode for the MOM capacitor structure, followed by a laserablation procedure, resulting in the formation of the desired high K,metal oxide component of the MOM capacitor structure. The laser ablationprocedure, performed in an oxidizing environment, allows the laserablated surface of the underlying metal layer to reach a temperatureneeded for formation of a dense, metal oxide region, while surroundingmetal structures, or metal structures used for non-MOM purposes, do notexperience the temperature increase. A second iteration of thisinvention features the subjection of localized regions of the underlyingmetal layer, to either UV or I line exposures. A photolithographic plateis used to allow only selective regions of the underlying metal layer tobe subjected to the UV or I line exposures, performed in an oxidizingenvironment, thus resulting in the formation of the desired metal oxidecomponent of the MOM capacitor structure, on an underlying metalelectrode structure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The object and other advantages of this invention are bestdescribed in the preferred embodiment with reference to the attacheddrawings that include:

[0011] FIGS. 1-8, which schematically, in cross-sectional style,describe key stages of fabrication used to form a high K dielectriclayer, for a MOM capacitor structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The methods used to form a high K dielectric layer for ametal-oxide-metal, (MOM), capacitor structure, featuring the use oflaser ablation, UV or I line exposure procedures, performed to anunderlying metal electrode component of the MOM capacitor structure, inan oxidizing environment, will now be described in detail. An interleveldielectric, (ILD), layer 1, comprised of either silicon oxide, undopedsilica glass, (USG), fluorinated silica glass, (FSG), orborophosphosilicate glass, is shown schematically in FIG. 1. Metal plugstructures 2, comprised of a metal chosen from a group containingtungsten, copper, or aluminum, are formed in via holes 20. Via holes 20,can expose underlying metal interconnect structures, or via holes 20,can be dummy openings, terminating at the top surface of an underlyinginsulator layer. A metal layer 3, comprised of either aluminum,tantalum, or copper, shown schematically in FIG. 2, is next depositedvia plasma vapor deposition, (PVD), procedures, to a thickness betweenabout 3000 to 5000 Angstroms.

[0013] The first iteration of this invention is next detailed anddescribed schematically in FIGS. 3-4. An in situ, laser procedure isperformed to local regions of metal layer 3, in an environment comprisedof either NO, N₂O, O₂, or O₃. The laser ablation procedure results inlocal heating of metal layer 3, confined to a region near the topsurface of metal layer 3. The localized heating, created by the laserspot, results in melting of metal layer 3, confined at the top surface,and in the presence of an oxidizing ambient, forms metallic dielectriclayer 4, consuming a portion of the of metal layer 3. The laser ablationprocedure is performed using excimer or YAG laser, at a power betweenabout 0.1 to 10 watts. The temperature reached, at the surface of metallayer 3, during the laser ablation procedure is between about 1000 to2000° C., while the surrounding device regions are not influenced by thesurface heating laser ablation procedure, and therefore remain attemperatures below 400° C. Metallic dielectric layer, or high K layer 4,is comprised of either Ta₂O₅, Al₂O₃, or CuO₂, at a thickness betweenabout 200 to 400 Angstroms, and with a dielectric constant between about22 to 35. The thickness of metal layer 3, after formation of high Klayer 4, is now decreased to between about 2500 to 4500 Angstroms. Thisis schematically shown in FIG. 3. An overlying metal layer 5, againcomprised of either aluminum, tantalum or copper, is next deposited viaPVD procedures, to a thickness between about 3000 to 5000 Angstroms.This is schematically shown in FIG. 4. Conventional photolithographicand RIE procedures, using Cl₂ or SF₆, as an etchant for the metallayers, while either BF₃, or CF₄/CHF₃ is used as an etchant for the highK layer, are employed to define metal-oxide-metal, capacitor structure6, schematically shown in FIG. 4.

[0014] A second iteration of this invention, featuring formation of thedesired high K layer, via use of UV or I line exposure, in an oxidizingambient, is next addresses, and schematically described in FIGS. 5-8.FIG. 5, shows metal plug structures 2 a, and metal plug structure 2 b,in via holes 20, where via holes 20, were formed in interleveldielectric layer 1. Metal layer 13, chosen from a group that includestitanium, tantalum, aluminum, or copper, is deposited via PVDprocedures, to a thickness between about 2500 to 4500 Angstroms. Aphotolithographic plate 15, comprised of quartz, with a chromium pattern16, is then situated, overlying metal layer 13. Opening 24, or thenon-chromium, clear region of photolithographic plate 15, willsubsequently define the region of metal layer 13, to be converted to thedesired high K layer. This is schematically shown in FIG. 5.

[0015] Exposure of metal layer 13, to a UV or to a I line, exposureconditions, in an ambient comprised of either O₂ or O₃, create high Klayer 18, in regions of metal layer 13, directly underlying opening 24,in photolithographic plate 15. The oxygen or ozone, flowing in space 7,in combination with the energy supplied by the UV or I line exposure,are sufficient to oxidize a top portion of exposed metal layer 13. Thisis accomplished using a UV exposure at an energy between about 1 to 100millijoules, while the exposure energy for the I line procedure is alsobetween about 1 to 100 millijoules. The oxygen or ozone flow, in thespace located between the photolithographic plate and the substrate, ismaintained between about 10 to 1000 sccm. The temperature reached at thetop surface of exposed metal layer 13, is between about 250 to 1000° C.,forming high K layer 18, at a thickness between about 200 to 300Angstroms, and reducing the thickness of the portion of metal layer 13,located underlying high K layer 18, to between about 2000 to 4000Angstroms. The dielectric constant of high K layer 18, comprised ofeither TiO₂, Al₂O₃, Ta₂O₅, or CuO₂, is between about 22 to 35. Theresult of selectively forming high K layer 18, in only a portion ofmetal layer 13, is schematically shown in FIG. 6. Again, as was the casefor the first iteration of this invention, the localized exposure ofonly a portion of the top surface of a metal layer, restricts theincrease in temperature to only the exposed area, maintaining lowertemperatures for the bulk of the device.

[0016] An overlying metal layer 19, comprised of either titanium,tantalum, aluminum, or copper, is next deposited, via PVD procedures, toa thickness between about 2500 to 4500 Angstroms, overlying high K layer18, and metal layer 13. Photoresist shapes 30, shown schematically inFIG. 7, are then formed on the regions of metal layer 19, for purposesof defining the metal-oxide-metal, capacitor structure, as well asdefining a metal interconnect structure. Anisotropic RIE procedures,using C1 ₂ or SF₆ as an etchant for metal layer 19, and for metal layer13, and using either BF₃, or CF₄/CHF₃ as an etchant for high K layer 18,are used to create capacitor structure 31, comprised of metal layer 19,high K layer 18, and metal layer 13, overlying, and contacting metalplug structures 2 a. This is schematically shown in FIG. 8. The same RIEprocedure results in the definition of metal interconnect structure 32,comprised of metal layer 19, and metal layer 13, communicating withactive device regions, such as underlying metal interconnect structures,(not shown in the drawings), via metal plug structure 2 b. Afterdefinition of these structures, photoresist shapes 30, are removed viaplasma oxygen ashing and careful wet cleans. If desired underlying metallayer 13, as well as overlying metal layer 19, can be comprised oftitanium, with a titanium nitride barrier layer, underlying metal layer13, and with another titanium nitride barrier layer, located overlyingmetal layer 19.

[0017] While this invention has been particularly shown and describedwith reference to the preferred embodiments thereof, it will beunderstood by those skilled in the art that various changes in form anddetails may be made without departing from the spirit or scope of theinvention.

What is claimed is:
 1. A method of forming a metal-oxide-metal,capacitor structure, on a semiconductor substrate, comprising the stepsof: depositing a first metal layer, on an underlying dielectric layer;performing an oxidation procedure to a top portion of said first metallayer to form a capacitor dielectric layer on a bottom portion of saidfirst metal layer, with said oxidation procedure producing in a highertemperature at the top surface of said first metal layer, than at otherregions of said semiconductor substrate; depositing a second metal layeron said capacitor dielectric layer; and patterning of said second metallayer, of said capacitor dielectric layer, and of said bottom portion ofsaid first metal layer, to form said metal-oxide-metal, capacitorstructure.
 2. The method of claim 1, wherein said first metal layer ischosen from a group that includes, titanium, tantalum, aluminum, orcopper, obtained via plasma vapor deposition, at a thickness betweenabout 3000 to 5000 Angstroms.
 3. The method of claim 1, wherein saidoxidation procedure is a laser ablation procedure, performed at a powerbetween about 0.1 to 10 watts, providing an oxidation temperature, atthe top surface of said first metal layer, between about 1000 to 2000°C.
 4. The method of claim 1, wherein said oxidation procedure, is a UVor I line exposure, performed to a portion of said first metal layer, atan energy between about 1 to 100 millijoules, resulting in a temperatureat the top surface of said first metal layer, between about 250 to 1000°C.
 5. The method of claim 1, wherein said oxidation procedure isperformed in an ambient chosen from a group that includes, O₂, O₃, NO,or N₂O.
 6. The method of claim 1, wherein said capacitor dielectriclayer is a metal oxide layer, chosen from a group that includes, TiO₂,Ta₂O₅, Al₂O₃, or CuO₂, at a thickness between about 100 to 400Angstroms.
 7. The method of claim 1, wherein said capacitor dielectriclayer has a dielectric constant between about 22 to
 35. 8. The method ofclaim 1, wherein said second metal layer is chosen from a group thatincludes aluminum, tantalum, titanium, or copper, obtained via plasmavapor deposition procedures, at a thickness between about 2500 to 4500Angstroms.
 9. A method of fabricating a high dielectric constant, (highK), layer, for a metal-oxide-metal, capacitor structure, via localizedoxidation of an underlying metal layer, using a laser ablationprocedure, comprising the steps of: depositing an underlying metallayer; performing said localized oxidation procedure, to a top portionof said underlying metal layer, via use of said laser ablationprocedure, performed in an oxidizing ambient, resulting in the formationof said high K layer, on a bottom top portion of said underlying metallayer; depositing an overlying metal layer on said high K layer; andpatterning of said overlying metal layer, of said high K layer, and ofunoxidized, said bottom portion of said underlying metal layer, to formsaid metal-oxide-metal, capacitor structure.
 10. The method of claim 9,wherein said underlying metal layer is chosen from a group thatincludes, titanium, tantalum, aluminum, or copper, obtained via plasmavapor deposition, at a thickness between about 3000 to 5000 Angstroms.11. The method of claim 9, wherein said laser ablation procedure isperformed at a power between about 1 to 10 watts, providing an oxidationtemperature, at the top surface of said underlying metal layer, betweenabout 1000 to 2000° C.
 12. The method of claim 9, wherein said oxidizingambient is chosen from a group that includes, O₂, O₃, NO, or N₂O. 13.The method of claim 9, wherein said high K layer is a metal oxide layer,chosen from a group that includes, TiO₂, Ta₂O₅, Al₂O₃, or CuO₂, at athickness between about 100 to 400 Angstroms.
 14. The method of claim 9,wherein said high K layer has a dielectric constant between about 22 to35.
 15. The method of claim 9, wherein said overlying metal layer ischosen from a group that includes aluminum, tantalum, titanium, orcopper, obtained via plasma vapor deposition procedures, at a thicknessbetween about 2500 to 4500 Angstroms.
 16. The method of claim 9, whereinsaid metal-oxide-metal, capacitor structure is patterned via ananisotropic RIE procedure, using Cl₂ or SF₆, as an etchant for saidoverlying metal layer, and for said underlying metal layer, while eitherBF₃, or CF₄/CHF₃ is used as an etchant for said high K layer.
 17. Amethod of fabricating a high dielectric constant, (high K), layer, for ametal-oxide-metal, capacitor structure, via exposure of a region of anunderlying metal layer, to a UV, or to an I line procedure, performed inan oxidizing ambient, comprising the steps of: depositing saidunderlying metal layer; performing said UV, or I line exposure, in saidoxidizing ambient, to a region of said underlying metal layer, exposedthrough clear regions of a photolithographic plate, creating said high Klayer, in a top portion of said underlying metal layer: depositing anoverlying metal layer on said high K layer, and patterning of saidoverlying metal layer, of said high K layer, and of unoxidized, bottomportion of said underlying metal layer, forming said metal-oxide-metal,capacitor structure.
 18. The method of claim 17, wherein said underlyingmetal layer is chosen from a group that includes, titanium, tantalum,aluminum, or copper, obtained via plasma vapor deposition, at athickness between about 3000 to 5000 Angstroms.
 19. The method of claim17, wherein said UV, or said I line procedure, is performed at an energybetween about 1 to 100 millijoules.
 20. The method of claim 17, whereinsaid oxidizing ambient is chosen from a group that includes, O₂, O₃, NO,or N₂O.
 21. The method of claim 17, wherein said high K layer is a metaloxide layer, chosen from a group that includes, TiO₂, Ta₂O₅, Al₂O₃, orCuO₂, at a thickness between about 100 to 400 Angstroms.
 22. The methodof claim 17, wherein said high K layer has a dielectric constant betweenabout 22 to
 35. 23. The method of claim 17, wherein said overlying metallayer is chosen from a group that includes aluminum, tantalum, titanium,or copper, obtained via plasma vapor deposition procedures, at athickness between about 2500 to 4500 Angstroms.
 24. The method of claim17, wherein said metal-oxide-metal, capacitor structure is patterned viaan anisotropic RIE procedure, using Cl₂ or SF₆, as an etchant for saidoverlying metal layer, and for said underlying metal layer, while eitherBF₃, or CF₄/CHF₃ is used as an etchant for said high K layer.